A chair having a one-piece shell of the type to which this invention can be applied is disclosed in U.S. Pat. No. 4,529,247. The disclosure of U.S. Pat. No. 4,529,257 is hereby included by reference as a part of this disclosure. The one-piece shell of this chair is molded from a high strength resilient plastic material, for example, fiberglass reinforced polyester resin. This chair provides postural support to a wide variety of people of different shapes and sizes through a variety of seated positions. The chair comprises a shell with a backrest and a seat pan integrally formed of structurally resilient material.
A U-shaped slot is formed in the seat pan. The bight portion of the U-shaped slot extends from the back of the seat pan along side portions thereof to define a cantilevered seat support that extends rearwardly from a forward portion of the seat pan. Seat webs extend rearwardly from the forward portion of the seat pan. The shell is mounted on a base in such a way that interference with the flexing of the cantilevered seat support is avoided. The cantilevered seat support reduces the shock of setting down, accommodates different shape users and adapts to the movements of the user in various postural relationships within the chair.
A U-shaped slot is also formed in the backrest of the one-piece shell near the side and lower portions thereof to form a cantilevered back support extending downward from an upper portion of the backrest. Back webs extend downwardly from the upper portion of the backrest adjacent the cantilevered back support. The backrest is of a shape and the shell is formed from material having sufficient rigidity and flexural strength such that the cantilevered back support and upper backrest support resiliently flex as a unit with respect to its integral connection to the seat pan. Thus, the backrest support automatically adjust to different size and shape persons and automatically accommodates different postural positions of the user in the chair.
In the preferred embodiment of the one-piece shell chair the U-shaped slots are joined at their bight portions to together form an H-shaped slot leaving flexure webs on each side of the shell between the seat support and the backrest support. The flexure webs joins with the seat webs and the back webs such that the backrest can resiliently flex with respect to the seat pan independently of the flexing of the cantilevered seat support and seat pan. Although the chair can be used in the shell form it may be covered with a foam cushion and/or fabric.
Although this chair can accommodate a variety of different shaped and sized people as a result of the flexibly suspended seat pan and backrest and can accommodate movements and shifts in the users positions some users become uncomfortable after setting in any chair especially after long periods of time. This is particularly true if the person setting in the chair is restricted in the postural positions that he or she can assume for reasons such as the work task that they are performing. The lumbar vertebrae, located in the small of the back and the surrounding muscles, tendons and ligaments are a common source of discomfort for a great many people after setting for prolonged periods. This source of discomfort can be precipitated by a person setting in a chair for long periods or setting in a chair in the same position for a long period of time.
For the foregoing reasons, there is a need for a one-piece shell chair in which the user of the chair can while seated in the chair change the contour of the backrest in the lumbar region to gain relief and avoid discomfort.
An inflatable support that can be secured to the backrest portion of an automobile seat is disclosed in U.S. Pat. No. 5,171,209. The inflatable support includes a rigid back element that is secured to the seat and to which a non-rigid inflatable element is secured. The non-rigid inflatable element is divided into two chambers that are interconnected by a mutual inflation and deflation tube. The two chambers are separated by a space that will be located in the spinal area of the person setting in the seat. The inflatable portions of the inflatable element are located such that they will engage the lumbar region of the person setting in the seat. An inflation pump, powered by an electric motor, periodically feeds pressurized air to the mutual inflation tube and thus to the two chambers. A deflation aperture is provide that will permit air to escape at a slower rate than it is provided by the inflation device to thus produce a cyclical inflation and deflation of the inflatable chambers. This reference requires a power source to periodically inflate the chambers and thus cause the chambers to pulsate. While, providing electric power in an automobile seat is feasible it is not desirable in for example an office chair. Also the support of this reference is stationary and cannot be adjusted vertically to change the location to which pressure is applied. Furthermore, the surface of the inflatable chambers is flexible and will not apply a uniform pressure over the contact area.
Co-pending application Ser. No. 449,898, filed May 23, 1995 discloses a co-planar multi-laminar mattress cushion and lumbar support system composed of a plurality of discrete chambers sealed to a fluid flow control panel which provides fluid flow conduits for inflation of the chambers. The invention of this application includes the concept of systematically inflating and deflating the discrete chambers so as to provide a constantly changing contour to the mattress cushion and lumbar support.